1. Field of the Invention
The present invention relates to a radiation image storage panel, and more particularly, to a radiation image storage panel improved in the resistance to physical deterioration such as abrasion.
2. Description of the Prior Art
For obtaining a radiation image, there has been conventionally employed a radiography utilizing a combination of a radiographic film having an emulsion layer containing a photosensitive silver salt material and an intensifying screen.
As a method replacing the above-described radiography, a radiation image recording and reproducing method utilizing a stimulable phosphor as described, for example, in U.S. Pat. No. 4,239,968, has been recently paid much attention. In the radiation image recording and reproducing method, a radiation image storage panel comprising a stimulable phosphor (i.e., a stimulable phosphor sheet) is employed, and the method involves steps of causing the stimulable phosphor of the panel to absorb a radiation energy having passed through an object or having radiated from an object; exciting the stimulable phosphor, or scanning the panel, with an electromagnetic wave such as visible light and infrared rays (hereinafter referred to as "stimulating rays") to sequentially release the radiation energy stored in the stimulable phosphor as light emission (stimulated emission); photoelectrically reading out the emitted light to obtain electric signals; and reproducing the radiation image of the object from the electric signals.
Since the radiation image storage panel employed in the method hardly deteriorates upon exposure to a radiation and stimulating rays, the panel can be employed repeatedly for a long period. In practical use, after scanning the panel with stimulating rays to release radiation energy as stimulated emission therefrom (otherwise, in advance of next use of the panel), light in the wavelength region of stimulating rays for the stimulable phosphor employed in the panel or heat is usually applied to the panel so as to erase the radiation energy remaining in the panel, because the stored radiation energy cannot be fully released from the panel by scanning with the stimulating rays.
In the above-described radiation image recording and reproducing method, a radiation image can be obtained with a sufficient amount of information by applying a radiation to an object at considerably smaller dose, as compared with the case of using the conventional radiography. Accordingly, this radiation image recording and reproducing method is of great value especially when the method is used for medical diagnosis.
The radiation image storage panel employed in the radiation image recording and reproducing method has a basic structure comprising a support and a stimulable phosphor layer provided on one surface of the support. Further, a transparent film is generally provided on the free surface (surface not facing the support) of the phosphor layer to keep the phosphor layer from chemical deterioration or physical shock. Furthermore, the edge faces of the panel may be reinforced by coating them with a polymer material to enhance the mechanical strength, as described in Japanese Patent Provisional Publication No. 58(1983)-68746 (corresponding to U.S. patent application Ser. No. 434,885 and European Patent Publication No. 83470).
As described above, the radiation image storage panel is employed repeatedly in a cyclic procedure comprising steps of erasing the remaining energy from the panel, exposing the panel to a radiation, and scanning the panel with stimulating rays (that is, reading out the radiation image as stimulated emission from the panel). In the above-mentioned cyclic procedure, the panel is transferred from a step to the subsequent step through a certain transfer system and generally piled on other panels to store after one cycle is finished.
Accordingly, the radiation image storage panel employed in the radiation image recording and reproducing method is subjected to conditions quite different from those to which the intensifying screen is subjected in the conventional radiography wherein the screen is fixed in a cassette. For this reason, various troubles which never occur in the use of the conventional intensifying screen are encountered in the use of the radiation image storage panel.
For instance, both surfaces of the radiation image storage panel are sometimes damaged by physical contact such as rubbing of the front surface of the panel against the back surface of another panel, or rubbing of the front surface (or back surface) of the panel against an edge of another panel, when the panel is piled on the other panel or moved from the pile of panels to the transfer system in the repetitious use comprising transfering and piling of the panel. Particularly, the physical damage occurring on the front surface is liable to cause scattering of stimulating rays, which results in decrease of an amount of image information to be obtained as well as obscuration of the image information.
Accordingly, it is desired for a radiation image storage panel which generally has a basic structure comprising a support, a phosphor layer provided on the support and a protective film provided on the phosphor layer as described above, that the front surface thereof (namely, the suface of the protective film) is protected to the utmost from the damage occurring in the transferring or piling procedure.